Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$5.86	13.265%	$6.6373	$6.64	$6.65	$6.60
Purchase #2	$163.81	5.373%	$172.6115	$172.61	$172.60	$172.60
Purchase #3	$40.48	4.869%	$42.451	$42.45	$42.45	$42.50
Purchase #4	$59.69	12.325%	$67.0468	$67.05	$67.05	$67.00
Purchase #5	$184.56	12.122%	$206.9324	$206.93	$206.95	$206.90
Purchase #6	$53.66	3.214%	$55.3846	$55.38	$55.40	$55.40
Purchase #7	$249.70	4.826%	$261.7505	$261.75	$261.75	$261.80
7 purchase totals =	$757.76		$812.8141	$812.81	$812.85	$812.80